Tap-changing device for transformers having load current diverter means and improved hydraulic follower mechanism therefor



March 19, 1968 BUHLER T 3,374,320 TAP-CHANGING DEVICE FOR TRANSFORMERS HAVING LOAD CURRENT DIVERTER MEANS AND IMPROVED HYDRAULIC FOLLOWER MECHANISM THEREFOR Filed 001'.- 24, 1966 Q l a A9 0 v l INVEEVTORS 1 Q!" 4 %Z l BY HGIHZ. Trachsel. v 2/ lid/w &Pa k..

United States Patent 3,374,320 TAP-CHANGING DEVICE FOR TRANSFORMERS HAVING LOAD CURRENT DIVERTER MEANS AND IMPROVED HYDRAULIC FOLLOWER MECHANISM THEREFOR Karl Biihler, Nussbaumen, and Heinz Trachsel, Ennet- Baden, Switzerland, assignors to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a jointstock company Filed Oct. 24, 1966, Ser. No. 588,824 Claims priority, application Switzerland, Nov. 2, 1965, 15,103/65 6 Claims. (Cl. 200-18) ABSTRACT OF THE DISCLOSURE A switching mechanism for diverting current when changing taps on a transformer comprises a multi-armed oscillatable diverter switch actuated when a tap change is made. One arm of the diverter switch controls a set of main contacts connected to the taps, two other arms control sets of quenching contacts in parallel with the main contacts and a fourth arm is articulated to piston elements of an oil-immersed hydraulic follower mechanism which includes a guide sleeve within which the pistons reciprocate, the guide sleeve itself also being reciprocated by the pistons within a stationary cylinder, and a contact arm articulated to the guide sleeve is oscillated by the latter to connect in a diverter resistance in the circuit of the main contacts.

The present invention relates to diverter switches for tap-changing switches of regulating transformers of the sort wherein the diverter switch consists of a main contact, a quenching (or load-switching) contact, and a lead contact for a diverter resistor, and the main and quenching contacts are rigidly coupled and are actuated in alternating directions by a driving arrangement.

It is known to use a diverter resistor when switching from one tapping to the next, in order to limit the circulating current. The lead contact used for this purpose switches the output side to the next tap prior to the actuation of the quenching contact. Since this must be so with every diverter switching, the quenching and lead contacts must be correspondingly actuated; In some diverter switches, arrangements are made whereby the quenching contact need not carry the operating current. In these cases it is bridged by a main contact which is actuated during the switch-over in such a way that it switches under no-load. In order to produce the desired contact sequence, mechanical arrangements have hitherto been used for the actuation of the contacts. However, these purely mechanical constructions have the drawback of requiring a comparatively large expenditure and of being rather complicated. In addition, wear is rather pronounced.

These drawbacks are avoided by the present invention. The invention has the object of providing a simple and cheap solution for actuating the lead contact, wherein the wear resistance is high, in accordance with the switching frequency of a tap changer. According to the invention, the lead contact, which leads in both directions of movement, is so connected with the remaining contacts by means of a hydraulic follower mechanism that the lead contact is retained in its end positions after these have been reached, whilst the remaining contacts are directly driven by the actuator until they reach their end positions. This affords a simple means for destroying the kinetic energy of the moving masses and of producing thereby the smooth entering into the end position, without necessitating special arrangements for this purpose.

The invention will be further explained, by way of example, with reference to the accompanying drawing, in which:

FIGURE 1 shows a diverter switch with a hydraulic follower device for the lead contact;

FIGURE 2 shows another embodiment of the follower device, which acts simultaneously as oil damper for the moving masses.

FIGURE 1 shows a transformer winding 1 equipped with several taps, two of which are shown at 2 and 3. Between the taps and the diverterswitch, there is a known tap selector which has been omitted from the drawing for the sake of clarity, and which is not required for the understanding of the invention. The star-shaped diverter switch part 4 is arranged to oscillate in a rotative manner in the directions of the arrows by a drive, not shown. Contact arms 5, 6 form, together with the resiliently mounted fixed contacts 7, 8 the quenching or load-switching contacts of the diverter switch. In addition, the part 4 has a further contact arm 9, which together with the contacts 10, 11 constitutes the main contacts, in parallel with the quenching contacts. The arm 9 is connected to the outlet u for the selected voltage. The lead contact consists of an insulating arm 13, pivoted at 12, and carrying a moving contact 14 which operates between fixed contacts 15, 16. The contact 14 and the junction u are connected through a diverter resistor 17. Furthermore the part 4 has an arm 18, to which is articulated at 19 a connecting rod 20 which is connected in turn with two opposed pistons 21. The pistons 21 fit closely in a slidable guide sleeve 22 which fits closely in a fixed cylinder 23'. The said guide sleeve 22 has lateral orifices 24 at each end immediately adjacent to its end covers and further openings 25 located further inwards. In addition, the lead contact 14 is pivotally connected at 26 to the guide sleeve 22. The whole assembly is immersed in oil.

When, for switching from the tap 2 to the tap 3, the part 4 is rotated in the direction of the solid-line arrow, arm 18 moves the two pistons 21 to the left; once the left piston 21 has passed beyond the orifice 25, the guide member 22 is carried along to the left, because the trapped oil inside the left-hand end of member 22 cannot escape. This causes the arm 13 to be carried along, moving about its pivot 12 and the contact 14 is lifted off the contact 15 in the direction of contact 16. This occurs substantially simultaneously with the lifting of the arm 9 off the contact 10, whilst the quenching contact 5, 7 opens somewhat later. The transmission ratio of the arms 9, 13, 18 is such that contact 14 switches to 16 before the arm 9 reaches the contact 11. When 14 has switched to 16, the larger diametered central portion of the guide sleeve 22 has come to rest against a stop shoulder 23a on the left side of the cylinder 23 and the left end orifices 24 are now open so that the pistons 21 can move to the left without further obstruction, because the previously trapped oil can now escape through the left-hand orifices 24. The lead contact 14 is therefore held whilst the remaining, directly driven, contacts can continue until they reach their end positions. The part 4 is arrested in its end positions by means of a device which is not shown and is known in the art. In addition, during that part of the switching when the lead contact 14 has already switched over but the other contacts have not yet reached their end positions, the lead contact 14 is held in position by the overpressure in the chamber to the left of the left piston 21 required to urge the oil out of the orifices 24. The low pressure in the space to the right of the right-hand piston 21 also urges guide sleeve 22 to the left to hold contact 14 in position: after a short travel of sleeve 22 the righthand orifices 24 are closed and it is only at the end of the travel that the right-hand orifices 24 are opened so that the said space can be again filled with oil.

During the next movement, the part 4 is rotated in the opposite direction as indicated by the arrow shown by a broken line. The lead contact 14 is again reversed at the start of the movement from contact 16 towards contact 15, because the hydraulic follower device constituted by elements 21 to 23 acts now in the opposite direction.

FIGURE 2 shows another hydraulic follower device in which the moving parts are braked in a simple manner during the last phase of the switching movement. To this end, the orifices 24 of the follower device, which is otherwise the same as described in conjunction with FIGURE 1, are positioned inwardly from their end caps by a certain amount towards the center and the pistons 21 are provided with an outlet groove 27. As may be seen, this arrangement is adapted to produce a desired braking curve in that the starting point and the magnitude of the braking may be chosen according to the positions and dimensions of the orifices and the outlet groove. This embodiment has the special advantage that a special oil damping device is no longer necessary.

We claim:

1. In a diverter switch for a tap-changing transformer, the combination comprising a set of main contacts having two stationary main contact members and a movable main contact member located therebetween, means for actuating said main movable contact member alternately in opposite directions so as to establish alternate engagement with said main stationary contacts, two sets of quenching contacts each of which includes stationary and movable contact members, said movable contact members of said quenching contacts being operated by said actuating means so as to effect disengagement therebetween subsequent to disengagement of said movable main contact member with a stationary main contact member, a set of lead contacts having two stationary lead contact members and a movable lead contact member located therebetween, each said stationary main contact member being electrically connected to a corresponding stationary quenching contact member and to a corresponding stationary lead contact member and to a corresponding tap point on said transformer, said movable main and quenching contact members being electrically interconnected, a diverter resistance connected between said main movable contact member and said movable lead contact member, and a reversible hydraulic follower device for actuating said movable lead contact member, said hydraulic follower device being controlled by said actuating means for said main and quenching contact sets and operable to hold said movable lead contact member engaged with one or the other of its stationary lead contact members until said movable main and quenching contact members reach their terminal positions in engagement with their respective stationary contact members.

2. A diverter switch for a tap-changing transformer as defined in claim 1 wherein said hydraulic follower means comprises an oil-submerged cylinder, a sleeve closed at its 4 ends and slidable within said cylinder, a pair of axially spaced pistons slidable within said sleeve, said pistons being connected to said actuating means for said main and quenching contact sets for reciprocating movement, said sleeve being connected to said movable lead contact member, and said sleeve being provided with end and intermediate ports controlling inflow and outflow of oil, said ports in conjunction with each said piston serving to trap oil within said sleeve between the piston and end wall of the cylinder during the initial movement of said piston thereby causing said sleeve to move with said piston and actuate said movable lead contact member to engage one of its stationary lead contact members prior to engagement of said movable main contact member with a stationary main contact member and further move ment of said piston and sleeve establishing communication between said end ports and the exterior of said cylinder thus to permit outward flow of the oil previously trapped within said sleeve, said sleeve then being stopped and movement of said piston continued.

3. A diverter switch for a tap-changing transformer as defined in claim 3 wherein each said piston includes a tapered outlet groove in the wall thereof cooperative with said end ports in said sleeve to effect a controlled braking action on said piston.

4. A diverter switch for a tap-changing transformer as defined in claim 3 wherein said actuating means for said movable main and quenching contact members is constituted by a four-armed rotationally mounted oscillatable member made of electrically conductive material, three of said arms having mounted respectively thereon said movable main and quenching contact members, and the fourth arm being connected to said pistons of said hydraulic follower device for actuating said movable lead contact member.

5. A diverter switch for a tap-changing transformer as defined in claim 1 wherein said hydraulic follower means includes means for effecting a braking action on the part thereof connected to said movable lead contact member.

6. A diverter switch for a tap-changing transformer as defined in claim 1 wherein said actuating means for said movable main and quenching contact members is constituted by a four-armed rotationally mounted oscillatable member made of electrically conductive material, three of said arms having mounted respectively thereon said movable main and quenching contact members, and i the fourth arm being connected to said hydraulic follower device for actuating said movable lead contact member.

No references cited.

ROBERT K. SCHAEFER, Primary Examiner.

I. R. SCOTT, Assisfant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,374 ,320 March 19 1968 Karl Biihler et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 53 the claim numbered "2" should be renumbered as claim -3 column 4, line 21, the claim numbered "3" should be renumbered as claim --4 line 26 the claim numbered "4" should be renumbered as claim S line 36, the claim numbered "5" should be renumbered as claim 2 Signed and sealed this 10th day of June 1969.

( E Attest:

EdwZi-d M. Fletcher, Jr. WILLIAM E SCHUYLER JR Attesting Officer 7 Commissioner of Patents 

